1. Technical Field
The invention relates to a radiating coaxial high-frequency cable with openings in the outer conductor which are in the form of slots arranged substantially perpendicular to the cable axis and which are configured in sections which are arranged consecutively without gaps in the longitudinal direction of the cable and whose axial length is dimensioned according to the high-frequency energy to be transmitted, wherein the number of slots is greater in the sections which are farther away from the feed location of the high-frequency energy than in the sections which are closer to the feed location.
2. Description of the Prior Art
Radiating coaxial high frequency cables--hereinafter called "RHF-cables--operate essentially as antennae as a result of the electromagnetic energy which is transmitted to the outside through the slots in the outer conductor. These cables enable communication between transmitters and receivers which move relative to each other. The intensity of the radiated power decreases along the length of the RHF cable due to cable damping (longitudinal damping) and because HF energy is radiated (coupling damping). Consequently, the so-called "system damping" which is the sum of the longitudinal damping and coupling damping--for example between an antenna of a vehicle and a RHF cable--increases with increasing cable length measured from the location where the HF energy is fed into the RHF cable. To keep the field strength which is received by a receiver moving along the RHF cable, at least approximately constant, the effect of the longitudinal damping of the RHF cable described in DE 41 06 890 A1 is compensated with the help of a special slot configuration. The number of the slots along the cable increases here according to a predetermined rule. The cable with this configuration can then made longer than a RHF cable with a uniform slot arrangement. Nonetheless, the length of the RHF cable along which a "usable" signal can be received or coupled in, remains relatively short, in particular at higher operating frequencies.
A conventional RHF cable can operate over a greater length by using the cable design according to EP 0 643 438 A1. This RHF cable has consecutive sections wherein each section has a different number of slots. The electrically effectual size of the openings formed by the slots increases with increasing distance from the location where the HF energy is injected into the cable. The longitudinal damping of the longer RHF cable is also compensated, providing greater flexibility for tuning important properties of the transmission system. The cable also requires a lesser number of amplifiers and feed locations along the cable run. This RHF cable has proven effective in practice. However, the "usable" length of the cable--as defined above--is still limited, in particular at higher frequencies.